On Tue, Jan 07, 2025 at 05:49:42PM +0800, Z qiang wrote: > > > > On Mon, Jan 06, 2025 at 11:24:54AM +0800, Z qiang wrote: > > > > > > > > On Fri, Jan 03, 2025 at 01:50:50PM +0800, Z qiang wrote: > > > > > > > > > > > > On Thu, Jan 02, 2025 at 01:41:16PM +0800, Oliver Sang wrote: > > > > > > > hi, Zqiang, hi, Paul, > > > > > > > > > > > > > > On Tue, Dec 31, 2024 at 08:19:44AM -0800, Paul E. McKenney wrote: > > > > > > > > On Tue, Dec 31, 2024 at 03:16:25PM +0800, Z qiang wrote: > > > > > > > > > > > > > > [...] > > > > > > > > > > > > > > > > > > > > > > > > > > > If you fix the issue in a separate patch/commit (i.e. not just a new version of > > > > > > > > > > the same patch/commit), kindly add following tags > > > > > > > > > > | Reported-by: kernel test robot <oliver.sang@xxxxxxxxx> > > > > > > > > > > | Closes: https://lore.kernel.org/oe-lkp/202412311203.ca7bddba-lkp@xxxxxxxxx > > > > > > > > > > > > > > > > > > > > > > > > > > > > Please try the following modifications: > > > > > > > > > > > > > > yes, the following modifications fix the issues we found for 9216c28c6a. thanks! > > > > > > > > > > > > > > Tested-by: kernel test robot <oliver.sang@xxxxxxxxx> > > > > > > > > > > > > Thank you, and I will apply this during my next rebase. > > > > > > > > > > > > Zqiang, unless you tell me otherwise, I will add your Co-developed-by > > > > > > and Signed-off-by. > > > > > > > > > > > > Either way, Happy Square New Year! > > > > > > > > > > Thank you, Happy New Year! :) > > > > > > > > And here you go! Please let me know of anything I missed. > > > > > > > > And thank you for saving me the time it would have taken to track > > > > this one down. ;-) > > > > > > > > Thanx, Paul > > > > > > > > ------------------------------------------------------------------------ > > > > > > > > commit 71c893e6d1857d1e4ea37aec557d734a560fdb39 > > > > Author: Paul E. McKenney <paulmck@xxxxxxxxxx> > > > > Date: Thu Dec 19 16:08:54 2024 -0800 > > > > > > > > srcu: Make SRCU readers use ->srcu_ctrs for counter selection > > > > > > > > This commit causes SRCU readers to use ->srcu_ctrs for counter > > > > selection instead of ->srcu_idx. This takes another step towards > > > > array-indexing-free SRCU readers. > > > > > > > > [ paulmck: Apply kernel test robot feedback. ] > > > > > > > > Co-developed-by: Z qiang <qiang.zhang1211@xxxxxxxxx> > > > > Signed-off-by: Z qiang <qiang.zhang1211@xxxxxxxxx> > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > > > Tested-by: kernel test robot <oliver.sang@xxxxxxxxx> > > > > > > > > diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h > > > > index c794d599db5c1..1b01ced61a45b 100644 > > > > --- a/include/linux/srcutree.h > > > > +++ b/include/linux/srcutree.h > > > > @@ -101,6 +101,7 @@ struct srcu_usage { > > > > */ > > > > struct srcu_struct { > > > > unsigned int srcu_idx; /* Current rdr array element. */ > > > > + struct srcu_ctr __percpu *srcu_ctrp; > > > > struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ > > > > struct lockdep_map dep_map; > > > > struct srcu_usage *srcu_sup; /* Update-side data. */ > > > > @@ -167,6 +168,7 @@ struct srcu_struct { > > > > #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name) \ > > > > { \ > > > > .sda = &pcpu_name, \ > > > > + .srcu_ctrp = &pcpu_name.srcu_ctrs[0], \ > > > > __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ > > > > } > > > > > > > > @@ -222,13 +224,12 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf); > > > > */ > > > > static inline int __srcu_read_lock_lite(struct srcu_struct *ssp) > > > > { > > > > - int idx; > > > > + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp); > > > > > > > > RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite()."); > > > > - idx = READ_ONCE(ssp->srcu_idx) & 0x1; > > > > - this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_locks.counter); /* Y */ > > > > + this_cpu_inc(scp->srcu_locks.counter); /* Y */ > > > > barrier(); /* Avoid leaking the critical section. */ > > > > - return idx; > > > > + return scp - &ssp->sda->srcu_ctrs[0]; > > > > } > > > > > > > > /* > > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > > > index d7ee2f345e192..3bf7f41ad72b8 100644 > > > > --- a/kernel/rcu/srcutree.c > > > > +++ b/kernel/rcu/srcutree.c > > > > @@ -253,8 +253,10 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) > > > > atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0); > > > > INIT_DELAYED_WORK(&ssp->srcu_sup->work, process_srcu); > > > > ssp->srcu_sup->sda_is_static = is_static; > > > > - if (!is_static) > > > > + if (!is_static) { > > > > ssp->sda = alloc_percpu(struct srcu_data); > > > > + ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0]; > > > > + } > > > > if (!ssp->sda) > > > > goto err_free_sup; > > > > > > ssp->srcu_ctrp should be assigned a value under the condition that > > > ssp->sda is allocated successfully. > > > > > > - if (!is_static) { > > > + if (!is_static) > > > ssp->sda = alloc_percpu(struct srcu_data); > > > - ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0]; > > > - } > > > if (!ssp->sda) > > > goto err_free_sup; > > > + if (!is_static) > > > + ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0]; > > > > It doesn't hurt to assign NULL to ssp->srcu_ctrp on allocation failure. > > > > Or am I missing something here? > > No, I just think in case of failed allocation, there is no need to set > srcu_ctrp. :) True enough, but you are adding an extra "if", which is not free from either an execution-time viewpoint (not an issue here) or from a complexity viewpoint. I am not ruling your change out, but neither am I convinced. Please see below for the current state, which passes light testing even given proper testing of _nmisafe(). Which I was failing to do before. Thoughts? Thanx, Paul ------------------------------------------------------------------------ commit e8964cf2179673adc54aae38b62361fd0fdf89ff Author: Paul E. McKenney <paulmck@xxxxxxxxxx> Date: Thu Dec 19 16:08:54 2024 -0800 srcu: Make SRCU readers use ->srcu_ctrs for counter selection This commit causes SRCU readers to use ->srcu_ctrs for counter selection instead of ->srcu_idx. This takes another step towards array-indexing-free SRCU readers. [ paulmck: Apply kernel test robot feedback. ] Co-developed-by: Z qiang <qiang.zhang1211@xxxxxxxxx> Signed-off-by: Z qiang <qiang.zhang1211@xxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Tested-by: kernel test robot <oliver.sang@xxxxxxxxx> diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index c794d599db5c1..1b01ced61a45b 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -101,6 +101,7 @@ struct srcu_usage { */ struct srcu_struct { unsigned int srcu_idx; /* Current rdr array element. */ + struct srcu_ctr __percpu *srcu_ctrp; struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ struct lockdep_map dep_map; struct srcu_usage *srcu_sup; /* Update-side data. */ @@ -167,6 +168,7 @@ struct srcu_struct { #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name) \ { \ .sda = &pcpu_name, \ + .srcu_ctrp = &pcpu_name.srcu_ctrs[0], \ __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ } @@ -222,13 +224,12 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf); */ static inline int __srcu_read_lock_lite(struct srcu_struct *ssp) { - int idx; + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp); RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite()."); - idx = READ_ONCE(ssp->srcu_idx) & 0x1; - this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_locks.counter); /* Y */ + this_cpu_inc(scp->srcu_locks.counter); /* Y */ barrier(); /* Avoid leaking the critical section. */ - return idx; + return scp - &ssp->sda->srcu_ctrs[0]; } /* diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index d7ee2f345e192..308cc7b5098c5 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -253,8 +253,10 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0); INIT_DELAYED_WORK(&ssp->srcu_sup->work, process_srcu); ssp->srcu_sup->sda_is_static = is_static; - if (!is_static) + if (!is_static) { ssp->sda = alloc_percpu(struct srcu_data); + ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0]; + } if (!ssp->sda) goto err_free_sup; init_srcu_struct_data(ssp); @@ -742,12 +744,11 @@ EXPORT_SYMBOL_GPL(__srcu_check_read_flavor); */ int __srcu_read_lock(struct srcu_struct *ssp) { - int idx; + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp); - idx = READ_ONCE(ssp->srcu_idx) & 0x1; - this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_locks.counter); + this_cpu_inc(scp->srcu_locks.counter); smp_mb(); /* B */ /* Avoid leaking the critical section. */ - return idx; + return scp - &ssp->sda->srcu_ctrs[0]; } EXPORT_SYMBOL_GPL(__srcu_read_lock); @@ -772,13 +773,12 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock); */ int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) { - int idx; - struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); + struct srcu_ctr __percpu *scpp = READ_ONCE(ssp->srcu_ctrp); + struct srcu_ctr *scp = this_cpu_ptr(scpp); - idx = READ_ONCE(ssp->srcu_idx) & 0x1; - atomic_long_inc(&sdp->srcu_ctrs[idx].srcu_locks); + atomic_long_inc(&scp->srcu_locks); smp_mb__after_atomic(); /* B */ /* Avoid leaking the critical section. */ - return idx; + return scpp - &ssp->sda->srcu_ctrs[0]; } EXPORT_SYMBOL_GPL(__srcu_read_lock_nmisafe); @@ -1152,6 +1152,8 @@ static void srcu_flip(struct srcu_struct *ssp) smp_mb(); /* E */ /* Pairs with B and C. */ WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); // Flip the counter. + WRITE_ONCE(ssp->srcu_ctrp, + &ssp->sda->srcu_ctrs[!(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0])]); /* * Ensure that if the updater misses an __srcu_read_unlock() @@ -2000,6 +2002,7 @@ static int srcu_module_coming(struct module *mod) ssp->sda = alloc_percpu(struct srcu_data); if (WARN_ON_ONCE(!ssp->sda)) return -ENOMEM; + ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0]; } return 0; }
